Adding a way to temporarily enable/disable ftrace_ops. The changefollows the same way as 'global' ftrace_ops are done.

Introducing 2 global ftrace_ops - control_ops and ftrace_control_listwhich take over all ftrace_ops registered with FTRACE_OPS_FL_CONTROLflag. In addition new per cpu flag called 'disabled' is also added toftrace_ops to provide the control information for each cpu.

When ftrace_ops with FTRACE_OPS_FL_CONTROL is registered, it isset as disabled for all cpus.

The ftrace_control_list contains all the registered 'control' ftrace_ops.The control_ops provides function which iterates ftrace_control_listand does the check for 'disabled' flag on current cpu.